At least one preferred embodiment of the present invention generally relates to a medical x-ray imaging system employing an electronic video camera that operates upon visible light to control brightness. At least one preferred embodiment of the present invention relates to an electronic video camera that utilizes a neutral density filter having varying opacity across the filter and that is adjustable for light attenuation.
In the past, medical diagnostic imaging systems have been proposed for imaging regions of interest in patients through the use of x-ray sources and receptors positioned on opposite sides of a patient""s region of interest. Typical x-ray imaging systems utilize an x-ray source and receptor that are movable to various positions relative to the patient""s region of interest. The x-ray source is controlled to adjust the amount of x-rays transmitted therefrom, passed through the patient and impinged on the x-ray receptor. X-ray receptors generally include an image intensifier having an x-ray detection layer that detects x-rays passing through a patient. The image intensifier converts the x-rays to visible light which is, in turn, guided onto an object plane proximate a video camera. The video camera includes an optical lens system focusing light from the object plane onto an image plane proximate a light sensitive sensor. One example of a light sensitive sensor is a charge coupled device. The light sensitive sensor detects and converts the visible light at the image plane data that is processed and ultimately displayed to a user.
Various anatomical regions attenuate x-rays to different degrees depending upon thickness, density, structure and the like of the anatomic region. These different characteristics of patient anatomy attenuate x-rays to different degrees and may degrade x-ray images where an anatomy of interest is located proximate certain other types of anatomy.
Operators of x-ray imaging equipment attempt to improve image quality of x-ray images through a variety of manners. One such manner for improving x-ray image quality involves adjusting the x-ray intensity transmitted by the x-ray source. For instance, anatomical regions that highly attenuate x-rays are imaged better by increasing the number of x-rays transmitted from the source. By increasing the x-ray transmissions, the user similarly increases the photon statistics sensed at the receptor (e.g., the number of photons impingent upon the image intensifier). As the photon statistics increase, the image intensifier converts more and more x-rays to visible light, thereby increasing the brightness of the light incident on the object plane of the electronic video camera. The light brightness may rise to a level sufficient to saturate the light sensor, such as the CCD. As the sensed light becomes excessive, the resulting processed and displayed image degrades. Image degradation may appear in several forms, such as a washed out image, an image having poor contrast between adjacent anatomies, and the like.
In the past, x-ray systems have attempted to prevent the light brightness from overloading the sensor by adding an iris to the electronic video camera having an adjustable opening passing only a desired amount of light. The diameter of the opening can be varied to affect the desired average attenuation of the brightness of the light at the object plane. As the system reduces the iris opening to xe2x80x9cstop downxe2x80x9d or partially close the iris opening, feedback sensing will detect that the average brightness of the light at the object plane is reduced, and the system can automatically increase the amount of x-rays impinging upon the receptor.
In accordance with the foregoing, the quality of the ultimately displayed image is influenced by the amount of x-ray flux (intensity) that is incident upon the image intensifier. The amount of light that is allowed to pass through the optics of the electronic video camera typically controls the amount of x-ray flux. A higher quality image requires more x-ray flux and more x-ray flux is permitted by decreasing the iris aperture that passes light through the camera optics, thereby avoiding sensor saturation. Motor controlled irises precisely control the amount of light passed through the optics in order to ensure that the minimum x-ray flux necessary is used in view of patient concerns. The iris aperture diameter and thus the amount of x-ray flux may be varied during single patient imaging procedure. Hence, light intensity is typically controlled automatically by the x-ray imaging system in accordance with commands from a user entered to initiate an imaging operation.
It is preferable that the electronic video camera only focus light near the object plane onto the image plane. The compact nature of x-ray systems typically results in the object plane and image plane being in close proximity to opposite ends of the camera optics. Hence, structure within the camera optics, such as glass surfaces and the like through which the light passes are located proximate the object plane. The glass surface and other transparent structure near the object plane may be focused by the camera optics onto the image plane as the iris aperture is reduced. These transparent structures in or near the camera optics may contain blemishes, such as scratches, digs and the like and may accumulate foreign material such as dirt. The blemishes and/or dirt may be close enough to the object plane as to become at least partially focused onto the image plane when the iris aperture is stopped down. The camera optics may partially focus images of the blemishes or dirt onto the image plane sufficiently that the light sensor at the image plane detects the blemishes/dirt as data conveyed to the processor to be imaged. These projections of blemishes and dirt create unwanted artifacts at the image plane that result as artifacts appearing in the displayed image.
FIG. 8 illustrates an exemplary configuration for the camera optics as formed in accordance with conventional systems. The camera optics 75 include a glass or other transparent layer 77 located at the input side to the camera optics proximate the object plane 79. The glass or other transparent layer 77 represents any kind of structure that could be part of the camera optics 75 such that this structure presents an opportunity for its surfaces to contain blemishes or dirt that may partially be in focus. For example, structure 77 could be part of the forward lens system 81, or structure 77 could be leaded glass installed for the purpose of reducing x-ray radiation beyond the optics such as would otherwise irradiate the optical sensor. The image intensifier directs light rays representative of an x-ray image onto the object plane 79. A forward lens system 81 is located proximate the glass layer 77 which directs light ray traces 83 and 86, from the object plane 79 through optical components 87 onto a rear lens system 89. The forward lens system also directs light ray traces 84 and 85 from blemishes/dirt in the glass layer 77 onto the rear lens system 89. The forward lens system 81 collimates the light ray traces 83-86, while the rear lens system 89 reconverges the light ray traces 83-86. The forward and rear lens systems 81 and 89 cooperate such that light ray traces 83 and 86 projecting from the object plane are collimated at the forward lens system 81 into a parallel manner and converged at the rear lens system 89 onto an image plane 91. When blemishes and dirt exist on the surface of the glass layer 77, light ray traces 84 and 85 are focused by the forward and rear lens systems 81 and 89 at a point 97
An adjustable iris 93 is opened and closed based upon the desired x-ray flux to control the amount of light ray traces passed therethrough onto the rear lens system 89. As the adjustable iris 93 reduces the opening therethrough, the shape and size of a focus region 95 proximate the image plane 91 expands. The focus region represents an area in which light rays are adequately in focus to be detectable at the image plane by the light sensor as a distinct image for which data is generated and processed (albeit possibly as an artifact). The size of the focus region 95 is relatively small when the iris 93 is open to a relatively large state. When in a relatively closed state (as illustrated in FIG. 8), the iris 93 forms a relatively large focus region 95 that includes light ray traces 84 and 85 projected from the surface of the glass layer 77. Hence, while the projection of blemishes and dirt are not focused directly on the image plane 91, the point 97 at which such blemishes and dirt are focused is adequately close to the image plane 91 to be sufficiently in focus at the image plane 91 that an artifact is created in the data generated by the light sensor. The partially focused images at the image plane 91 of dirt and other blemishes are detected by the sensor, processed and displayed along with the x-ray image. The image portions associated with the dirt and blemishes appear as artifacts in the resulting x-ray image. Hence, reducing the iris aperture may increase the tendency of dirt or blemishes close to the object plane to manifest themselves on the image plane.
A need remains for an improved x-ray imaging system and electronic video camera apparatus that avoids the disadvantages discussed above, while permitting x-ray flux to be increased when desired to obtain a higher quality image.
In accordance with at least one embodiment of the present invention, in a medical x-ray imaging system, an electronic video camera is provided for focusing light rays from an object plane proximate an image intensifier onto an image plane proximate a light sensor. The electronic video camera includes an object plane receiving light rays representative of a patient image. A lens system is provided between the object plane and image plane to focus the light rays from the object plane onto the image plane. An optical filter is also located between the object and image planes. The optical filter attenuates or partially blocks the light rays. The optical filter includes at least first and second filter regions having different opacity. The first and second filter regions are alignable with the lens system at different times to block different amounts of light rays associated with differing x-ray intensities that are transmitted at different times.
In accordance with at least one alternative embodiment, the optical filter includes a neutral density wheel having first and second sectors with differing thicknesses of opaque material deposited thereon to form the first and second filter regions. Optionally, the optical filter may include a circular filter having multiple sectors located adjacent one another. The sectors may have different opacities. Optionally, the optical filter may include filtered discs having at least two non-overlapping sectors of different opacity where the opacity is constant throughout each sector. As a further option, the optical filter may attenuate light passing there through to different degrees based on a rotational orientation of the optical filter with respect to the lens system.
In accordance with at least one embodiment, at least a portion of the first filter region is formed to be highly transparent to light rays and at least a portion of the second filter region is formed to have increasing opacity at progressively larger angular orientations of the optical filter with respect to a reference plane traversing the lens system. Optionally, the optical filter may be formed with a continuously varying opacity. The optical filter may variably attenuate the amount of light rays passed through the lens system based upon the position at which the optical filter is set relative to the lens system. Optionally, the optical filter may include a wheel located such that a sector of the wheel aligns with the lens system. The sector of the wheel aligned with the lens system represents one of the first and second filter regions. The wheel may have an opacity that continuously varies as a function of the angular orientation of the wheel with respect to the lens system.
Optionally, the optical filter may be formed with uniform opacity over discrete non-overlapping sectors where each discrete sector has a unique opacity that differs from other sectors by an amount based on an orientation of the optical filter with respect to the lens system. Optionally, the optical filter may include two filter wheels aligned with one another and having similar but opposite variations in opacity at progressively greater angular positions about the filter wheels.
In an alternative embodiment, the lens system may include forward and rear lens assemblies spaced apart from one another with the optical filter being positioned there between. Optionally, an iris may be located between the optical filter and the object plane with the iris including an aperture controlling a brightness of the light rays impingent upon the optical filter. The iris maintains a constant aperture at numerous x-ray intensities. Optionally, an electrical motor may be provided to adjust the position of the optical filter with respect to the lens system to automatically adjust attenuation of light rays by moving the optical filter between first and second positions to move the first filter region to an unused position and the second filter region to an operative position.
In accordance with at least one alternative embodiment, a medical x-ray system is provided having a support structure holding an x-ray source and receptor facing one another and aligned along a patient imaging axis. The x-ray source and receptor cooperate to obtain x-rays attenuated by a patient region of interest. The x-ray source may be controlled to vary an intensity of transmitted x-rays. The receptor converts x-rays to light rays representative of the patient region under examination, such that a brightness of the light rays varies based on the intensity of the x-rays received at the receptor. A processor processes the light rays to obtain x-ray images and a display displays processed x-ray images. A partially opaque member is provided to block a portion of the light rays to reduce a brightness of the light rays. The partially opaque member is provided with regions of different opacity.
In accordance with at least one embodiment, a motor assembly is provided for automatically moving the partially opaque member to vary the amount of attenuation of the brightness of the light rays. Optionally, means may be provided for shifting the partially opaque member from a highly opaque state to a lesser opaque state causing a reduction in an intensity of x-rays transmitted from the x-ray source until the average brightness of the light incident on the image sensor is reduced to the proper level.
Alternatively, a motor and gear assembly may be provided to rotate the partially opaque member between first and second angular positions to move a more opaque region of the partially opaque member into alignment with the light rays. Optionally, an assembly may be provided for moving the partially opaque member between an initial position at which light rays pass through a highly transparent portion of the partially opaque member to a final position at which a portion of the light rays are blocked by a highly opaque portion of the partially opaque member. Optionally certain regions of the partially opaque member may be provided with constant opacity. Optionally, regions of the partially opaque member may be provided with continuously varying opacity.